INTRODUCTION: QT prolongation and obesity are associated with ventricular arrhythmia and sudden cardiac death. The relationship between uncomplicated obesity and QT interval prolongation is not clear. OBJECTIVES: The aim of the study was to investigate the effects of uncomplicated obesity on QT interval in young men. PATIENTS AND METHODS: A total of 122 men, including 59 obese patients and 63 controls, were recruited into the study. Patients with hypertension, diabetes mellitus, and ischemic heart disease were ineligible. Body mass index (BMI) of all patients was calculated. QT interval was measured from the precordial lead--V5, and corrected QT (QTC) was calculated using the Bazett's formula. RESULTS: Mean age, BMI, and waist circumference (WC) of obese patients and controls were as follows: 22.0 +/-3.0 years, 36.2 +/-2.2 kg/m(2), and 114 +/-8.1 cm; 22.6 +/-2.9 years, 24.7 +/-2.5 kg/m(2), and 81.6 +/-7.5 cm, respectively. There was a statistically significant difference between the obese and control groups with regard to BMI and WC (P <0.001). Furthermore, statistically significant differences were observed between the 2 groups in terms of QTC (407.9 +/-17.1 ms vs. 397.7 +/-14.0 ms, respectively, P <0.001), systolic (126.9 +/-8.2 mmHg vs. 114.2 +/-11.1 mmHg, respectively, P <0.001) and diastolic blood pressure (78.3 +/-4.5 mmHg vs. 66.9 +/-10 mmHg, respectively, P <0.001). There was a positive correlation between QTC interval and both WC (r = 0.357, P <0.001) and BMI (r = 0.424, P <0.001). There was no association between QTC and blood pressure. CONCLUSIONS: Uncomplicated obesity in young men is associated with QT interval prolongation. Weight gain may inversely affect cardiac repolarization in uncomplicated obesity.